Sometimes the map files are just to big to sit there and download from any server. So here is a full list of whitelisted maps located on the tripwire forums.
http://forums.tripwireinteractive.com/showthread.php?t=41919Just press ctrl+f and then type the map name you are looking for.
Once you have found the map download it and extract it.
After you open it up you should see a ROM file
Take that ROM file and put it in your Killing Floor maps folder located at C:\Program Files\Steam\steamapps\common\killingfloor\Maps
Then you are all set.